Bitter rivals Kamala Harris and Donald Trump are embarking on a final frenzied campaign blitz with both hitting must-win Pennsylvania on the last day of the tightest and most volatile US presidential election in memory, AFP reports.

On the eve of Election Day, polls suggest a total deadlock in surveys nationally and in the seven swing states where the result is expected to be decided.

Harris will spend the whole day campaigning in the rust-belt state of Pennsylvania, culminating in a huge rally in its biggest city Philadelphia featuring singer Lady Gaga. Trump will travel to North Carolina, Pennsylvania and then Michigan.

In a sign of how crucial Pennsylvania is to their chances of occupying the Oval Office, Trump and Harris will even hold duelling rallies in the industrial city of Pittsburgh. Pennsylvania is the single biggest swing state prize under the US Electoral College system, which awards influence in line with population.